Imagine a city of 12 million people, all on bicycles. No cars. Imagine walking across Tienanmen (天安門) square to the Forbidden City, in the dead of winter, and not a soul is there. Imagine taking an old 'Shanghai' taxi out to the Great Wall in February, and you are the only person standing in the snow-swept landscape. Imagine mid-summer on the city's biggest shopping street, Wangfujing, and everyone - everyone - is wearing white. Imagine Beijing in 1979.